<ul style="padding:0 5px;background: rgb(228, 196, 215)">
  <li routerLink="threeChild1" routerLinkActive="activeChild">threeChild1</li>
  <li routerLink="threeChild2" routerLinkActive="activeChild">threeChild2</li>
  <li routerLink="threeChild3" routerLinkActive="activeChild">threeChild3</li>
</ul>
<router-outlet></router-outlet>